U.S. patent number 5,834,921 [Application Number 08/886,535] was granted by the patent office on 1998-11-10 for safety device for a portable battery-powered electric apparatus.
This patent grant is currently assigned to Telefonaktiebolaget LM Ericsson. Invention is credited to Bjorn Frannhagen, Johan Mercke.
United States Patent |
5,834,921 |
Mercke , et al. |
November 10, 1998 |
Safety device for a portable battery-powered electric apparatus
Abstract
A safety device for a portable battery-powered electric
apparatus having a battery unit with one or more battery cells for
supplying power to electric circuitry in the apparatus. The
apparatus is connectable to a charging device for charging the
battery unit while maintaining the supply of power to the
apparatus. The safety device has a first fuse device connected
between the battery unit and a first terminal of the apparatus for
receiving charging current from the charging device, and a second
fuse device connected between the battery unit and a second
terminal of the apparatus for supplying power to electric circuitry
in the apparatus. The fuse devices are operatively independent of
each other, particularly in that the second fuse device maintains
the electric connection between the battery unit and the electric
circuitry in the apparatus, even when or if the first fuse device
releases or opens in response to an undesired condition in the
charging device.
Inventors: |
Mercke; Johan (Lund,
SE), Frannhagen; Bjorn (Lund, SE) |
Assignee: |
Telefonaktiebolaget LM Ericsson
(SE)
|
Family
ID: |
26662699 |
Appl.
No.: |
08/886,535 |
Filed: |
July 1, 1997 |
Current U.S.
Class: |
320/112; 320/128;
320/154; 361/104; 361/106; 361/103; 307/66; 320/150; 320/DIG.13;
320/134 |
Current CPC
Class: |
H02J
7/0031 (20130101); H02J 7/0068 (20130101); Y10S
320/13 (20130101) |
Current International
Class: |
H02J
7/00 (20060101); H02J 007/00 () |
Field of
Search: |
;320/150,154,134,112,116,DIG.13,128 ;361/104,103,106
;307/66,67 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
553 824 |
|
Aug 1993 |
|
EP |
|
2 239 567 |
|
Jul 1991 |
|
GB |
|
WO96/36098 |
|
Nov 1996 |
|
WO |
|
Primary Examiner: Wong; Peter S.
Assistant Examiner: Shin; K.
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis,
L.L.P.
Claims
What is claimed is:
1. A safety device for a portable battery-powered electric
apparatus having a battery unit with at least one battery cell for
supplying power to electric circuitry in the apparatus, the
electric apparatus being arranged to be connected to a charging
device for charging the battery unit while maintaining the supply
of power to the electric apparatus, comprising:
a first fuse arranged to be connected between the battery unit and
a first terminal of the electric apparatus for receiving charging
current from the charging device, and
a second fuse arranged to be connected between the battery unit and
a second terminal of the electric apparatus for supplying power to
electric circuitry in the electric apparatus,
wherein the first and second fuses are operatively independent of
each other, particularly in that the second fuse can maintain an
electric connection between the battery unit and the electric
circuitry in the apparatus even if the first fuse opens in response
to an undesired condition in the charging device.
2. The safety device of claim 1, wherein the first and second fuses
are physically integrated.
3. The safety device of claim 1, wherein the first and second fuses
are formed as layers of a material that is active with respect to
at least one physical property, the layers are arranged between a
contact tab and a first contact and a second contact, respectively,
the contact tab is arranged to be connected to the battery unit,
the first contact is arranged to be connected to the first
terminal, and the second contact is arranged to be connected to the
second terminal.
4. The safety device of claim 3, wherein an electrical conductivity
of the material in a direction between the contact tab and the
first and second contacts, respectively, is substantially zero when
a temperature of the material exceeds a predetermined upper
threshold value and returns to a non-zero value when the
temperature of the material falls below a predetermined lower
threshold value.
5. The safety device of claim 3, wherein the first and second
contacts have planar upper surfaces for receiving a respective
resilient contact of the electric apparatus.
6. The safety device of claim 5, wherein a third contact is mounted
on the contact tab by an intermediate layer of an electrically
isolating material, which has a planar upper surface for receiving
a third resilient contact of the electric apparatus, and which is
arranged to be connected to a negative side of the battery unit
while the contact tab is arranged to be connected to a positive
side of the battery unit.
7. The safety device of claim 1, wherein the electric apparatus is
a mobile telephone for a cellular mobile telephone system.
8. A rechargeable battery unit having at least one battery cell for
supplying power to a portable electric apparatus, wherein the
battery unit comprises a safety device according to claim 1.
Description
TECHNICAL FIELD
The present invention relates to a safety device for a portable
battery-powered electric apparatus, the apparatus comprising a
battery unit for supplying power to electric circuitry in the
apparatus and being connectable to a charging device for charging
the battery unit while maintaining the power supply of the
apparatus.
BACKGROUND
Rechargeable batteries are used in various portable applications,
such as cellular telephones, communication radio devices, laptop
computers, videocameras, etc. Throughout this document the
discussion and description will relate to the first example above,
i.e. cellular telephones. However, this does not limit the
invention to cellular telephones only; on the contrary, a man
skilled in the art will realize, when considering the description
below, that the invention may be applied in various related
technical fields.
In the applications above a rechargeable battery consists of a
plurality (preferably 2-5) of battery cells, which are connected in
series so as to provide an external supply voltage of between, for
instance, 3 and 6 volts, as desired. Such a battery unit comprises
additional components, such as connection terminals, contact tabs,
battery housing and fuses. Conventionally, NiCd (nickel-cadmium)
battery cells have been frequently used, but recently NiMH
(nickel-metal hydride) cells and Li cells (lithium-iron,
lithium-polymer) have become more common. Regardless of the battery
type, and for reasons of comfort, the battery may often be
connected to a charging device for supplying charging current
thereto, without having to remove the battery from e.g. the
cellular telephone. Furthermore, due to user demands the battery
may usually be charged without having to turn off the cellular
telephone or remove it from service.
FIG. 1 discloses a schematic block diagram for a charging
arrangement according to the prior art. A number of battery cells
13a, 13b (in this case: two battery cells) are according to above
connected in series and constitute a battery unit 12. The battery
unit 12 is arranged to supply power to a cellular telephone 11,
which may be chosen from any of the models available on the market
and which is hence schematically indicated only by a dashed line.
The cellular telephone comprises various electric and electronics
circuits and components, such as power amplifiers, microprocessor,
filter circuits, local oscillators, etc. The presence of these
circuits and components is obvious to a man skilled in the art, and
hence the components are only represented by a common block of
electronics 14.
The battery unit 12 has two connections: a positive terminal and a
negative terminal. To protect the battery the battery cells 13a,
13b are connected in series with a fuse 18, which will normally be
resetable.
A charging device 16 is arranged to be attached via connections in
the telephone 11 to the battery unit 12 for charging purposes. As
appears from the drawing, the battery may be charged while the
mobile telephone 11 is maintained in operation, which according to
the above is a common user demand. A major disadvantage of a
charging arrangement according to FIG. 1 is that if the charging
device for some reason would supply an excessively strong charging
current to the battery unit 12, wherein the fuse 18 would open as a
consequence thereof, then the voltage across the block of
electronics 14 in the mobile telephone would rise to a dangerously
high level, where the circuits and components in the block 14 may
be damaged or completely destroyed. For this reason at least one
additional fuse 19a and 19b, respectively, (or some other kind of
suitable protection means) is required inside the charging device
16 and the mobile telephone 11, respectively. Such multiple-fuse
safety arrangements require additional space and lead to an
increase in manufacturing costs.
FIG. 2 illustrates a fuse 18 according to the prior art. A thin
layer of an active material 17 is interposed between two metallic
contact tabs 15a, 15b. The active material 17 consists of a
polymeric material and comprises thin carbon fibres, which normally
conduct electric current between the contact tabs 15a, 15b. When
the magnitude of the current increases due to an electric fault,
the generation of heat in the active material 17 will increase as a
consequence. The rising temperature in the material causes an
expansion of the material, wherein the carbon fibres will separate
and interrupt the electric connection between the contact tabs. The
fuse is automatically resetable, since the carbon fibres will
regain contact, once the material has cooled down.
Previously known battery units are shown in for instance GB-A-2 239
567, U.S. Pat. Nos. 4,578,628, 4,916,594 and 4,555,451. Examples of
useful fuses are found in U.S. Pat. Nos. 4,563,628, 5,367,280 and
5,146,150, among others.
SUMMARY
The object of the present invention is to provide effective and
reliable charging of the battery unit in a portable electric
apparatus, such as a cellular telephone, with a minimum of
components and at a low cost of material. The invention is
particularly aimed at eliminating the risk of damaging the
electronics comprised in the apparatus due to an excessively high
supply voltage, when the charging process deviates from the normal
situation, for instance due to the release of a fuse in the battery
unit.
The object is achieved by a safety device that includes a first
fuse device, which is arranged to be connected between a battery
and a first terminal of an apparatus powered by the battery for
receiving charging current from a charging device, and a second
fuse device, which is arranged to be connected between the battery
and a second terminal of the apparatus for supplying power to
electric circuitry in the apparatus. The first and second fuse
devices are operatively independent of each other, particularly in
that the second fuse device maintains the electric connection
between the battery and the electric circuitry in the apparatus,
even when or if the first fuse device releases or opens in response
to an undesired condition in the charging device.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail in the
following, reference being made to the accompanying drawings, in
which
FIG. 1 is a schematic block diagram of a known charging arrangement
for a mobile telephone,
FIG. 2 discloses a known fuse, which is used in the arrangement
according to FIG. 1,
FIG. 3 is a schematic block diagram of a charging arrangement for a
mobile telephone, in which the safety device according to the
invention is used,
FIG. 4 illustrates one embodiment of the safety device according to
the invention, as disclosed in FIG. 3, and
FIG. 5 illustrates an alternative embodiment of the safety device
in FIG. 3 .
DETAILED DISCLOSURE
As previously mentioned, a known charging arrangement is shown in
FIGS. 1 and 2 as well as an example of a fuse used therein.
In FIG. 3 a charging arrangement is shown, wherein a safety device
10 according to a preferred embodiment of the present invention is
used. As in FIG. 1, a charging device 16 is arranged to supply
charging current to a battery unit 12 attached to a mobile
telephone 11 for charging the battery unit. The charging device 16
and the mobile telephone 11 with its electronic components 14 are
essentially identical to the ones already described with reference
to FIG. 1, and hence the disclosure thereof is not repeated.
The battery unit 12 comprises a plurality--here: two--of battery
cells 13a, 13b of an arbitrary type (such as NiMH, Li-type or
NiCd), said cells being connected in series so as to provide a
sufficient level of an external supply voltage for driving the
electronic components 14. A difference compared to FIG. 1 is that
the battery unit 12 is now provided with three terminals: a
negative terminal, a first positive terminal and a second positive
terminal. The first positive terminal is protected by a first fuse
means 20 and is arranged to be connected to a first (positive)
terminal 24 of the mobile telephone 11, while the second positive
terminal is protected by a second fuse means 21 and is arranged to
be connected to a second (positive) terminal 26 of the mobile
telephone. Finally, the negative terminal is arranged to be
connected to a third (negative or ground) terminal 40 of the mobile
telephone 11.
The battery unit 12 is arranged to receive charging current from
the charging device via the terminal 24. In addition, the battery
unit is arranged to supply charging current to the mobile telephone
11 through the terminal 26. The following advantages are obtained
thanks to the inventive arrangement of terminals and fuse means
described above.
If the charging device 16 no longer operates normally but instead
supplies an excessively strong charging current, or is subject to a
short circuit, only the first fuse means 20 will release. This will
abort the charging, but the second fuse means 21 will still be
operative, wherein the power supply of the mobile telephone will
not be affected.
The need for an additional fuse 19a in the charging device 16 or an
additional fuse 19b in the mobile telephone 11 (see FIG. 1) is
eliminated thereby providing an advantage from an economical point
of view.
The arrangement above allows the two fuse means to be realized as
an integrated safety device 10, which will be closer described
below with reference to FIG. 4.
In FIG. 4 a preferred embodiment of the safety device 10 according
to the invention is shown. A thin layer of an active material 36 is
deposited on a metallic contact tab 30, which is arranged to be
connected in series with the battery cells 13a-b by means of
soldering, laser or spot welding, etc. The active material 36 is a
polymeric material, comprising thin fibres of carbon or another
conductive material, said fibres normally conducting electric
current but will separate in space and interrupt the current path,
once the magnitude of the current increases as a result of an
electric fault (cf. the description above with reference to FIG.
2). Hence, the material 36 is active in that the status thereof as
a conductor of electric current is dependent on a physical
property--in this case the current magnitude indirectly via the
temperature of the material. The active material is known per se in
the technical field, and hence a thorough disclosure will not be
necessary here.
Two contact plates 32 and 34, respectively, are arranged upon the
layer of active material 36. Preferably, these are made from metal
and are provided with a smooth upper surface suitable for
engagement with the corresponding terminals 24 and 26 in the mobile
telephone 11. In the drawing the terminals 24 and 26 are formed as
spring contacts, which are arranged to be resiliently pressed
against a respective contact 32 and 34 in the safety device 10.
By providing the safety device 10 with double safety functions on
the same substrate according to the preferred embodiment the
problems described above are solved in an efficient way with
respect to cost as well as space. Since the safety device is
automatically resetable, the battery unit requires no maintenance
in this respect.
FIG. 5 illustrates an improvement of the embodiment shown in FIG.
4. Components which are identical in FIG. 4 and FIG. 5 have been
given identical reference numerals in both figures. The safety
device 10 according to FIG. 5 has been provided with an additional
contact means 42, which is arranged on an electrically isolating
layer 44. The layer 44 is arranged on the contact tab 30, and so is
the layer 36 of active material. The contact means 42 has a smooth
upper surface for the reception of a third resilient contact means
40 in the mobile telephone 11. The contact means 42 is arranged to
be soldered, welded or in any other way connected to the negative
side of the battery cells 13a-b, while the contact tab 30 as before
is arranged to be connected to the positive side of the battery
cells.
Within the scope of the invention, as defined in the subsequent
patent claims, the safety device may be realized in other ways than
the ones described above, which should be readily realized by a man
skilled in the art. For instance, instead of the active polymeric
material, an arrangement with bimetallic elements may be used.
Furthermore, the safety device does not necessarily have to be
automatically resetable, although such a feature is regarded to be
appropriate. Finally it is noticed once again, that the invention
may be used together with electric equipment other than mobile
telephones.
* * * * *